1. Field of the Invention
The present invention relates to an apparatus for treating evaporative fuel (fuel vapor) in which fuel evaporated within a fuel storage chamber such as, for example, a fuel tank of a vehicle, is subjected to adsorption treatment to prevent direct emission of evaporated fuel into the atmosphere.
2. Description of the Prior Art
An apparatus is known, as disclosed, for example, in Japanese Utility Model Publication laid open No. 23458/1986, in which, in order to prevent fuel vapors which naturally form within a vehicle's fuel tank from being scattered into the atmosphere, a canister is placed at a bottom of the fuel tank and connected to the fuel tank. An adsorbing material such as activated carbon is stored within the canister. To enhance the adsorbing performance of the material stored in the canister, cool feeding fuel is circulated to the bottom of the fuel tank to cool the canister. However, the canister arrangement shown in that publication is low in adsorbing ability. It adsorbs only fuel vapors that are evaporated within the fuel tank during normal running of the vehicle.
It has been recently found that a considerable amount of fuel vapor is generated at the time of gasoline feeding (when the fuel tank is being filled). This fuel vapor escapes into the atmosphere and contaminates it. It is also harmful to human beings. Therefore, it is desireable to provide an arrangement that has the ability to treat fuel vapors that are generated at the time of fuel feeding. If an attempt is made to adsorb the evaporative fuel by the canister arrangement known in the prior art, a large amount of fuel adsorbing material is required because a great amount of evaporative fuel generated during gasoline feeding. Thus, a large-size canister has to be used, posing a structural problem of mounting it on the vehicle.
Moreover, the fuel vapor generated at gasoline feeding is generated rapidly and must therefore be adsorbed in a short period of time. When evaporative fuel is adsorbed in a short period of time, there is much heat of adsorption which causes the temperature of the fuel adsorbing material to increase quickly. The increase of temperature of the fuel adsorbing material deteriorates its adsorbing ability.
It has also been recently found that adsorbing and de-adsorbing performances of such materials are greatly influenced by canister temperature. When the canister is cooled, the adsorbing performance is enhanced and conversely, when the canister is warmed, the de-adsorbing performance of the adsorbed fuel is enhanced. The structural arrangement of the prior art does not have sufficient heat exchanging capacity between the canister and the feeding fuel to adequately cool the fuel adsorbing material at gasoline feeding. When the engine is operated, the canister temperature is substantially the temperature of its environment, i.e. the temperature in the fuel tank. The canister temperature is not significantly cooled by incoming fuel to enhance adsorbing performance or warmed to enhance de-adsorbing performance.
The present invention provides an apparatus for treating evaporative fuel that has a relatively small and simple mechanical structure and provides a marked improvement in adsorbing and de-adsorbing performance with respect to prior art devices.